This application is a continuation-in-part of application Ser. No. 12/410,496, filed Mar. 25, 2009.
The present invention relates generally to mine roof cable bolt assemblies and components thereof operable to support roofs in underground coal mines and other underground facilities.
Underground coal mines often are hazardous environments, and preventing a roof collapse is a top priority of mining companies. Generally, two products are used to support a roof—roof bolts, and roof cables. Roof bolts are the primary support for the roof; however, over time, mining companies have installed roof cables in boreholes drilled into the roof, with roof bearing plates at an end thereof. These cable systems have been installed to support the roof in the event of a roof bolt failure, and are not designed or installed to provide an immediate supportive, compressive force against the roof (until the roof bolts begin to fail, and the roof begins to drop).
At least one device has attempted to support the roof with a roof cable upon installation and prior to a failure of a roof bolt, as described in U.S. Pat. No. 6,402,433 to Gillespie. This patent discloses a roof cable having a cable with a head end formed of an externally threaded outer sleeve, where the cable bolt shaft has an enlarged section that is slightly larger than the internal diameter of the bolt head outer sleeve so that the cable interferes with the bolt head outer sleeve as the cable is pressed into the outer sleeve to form the cable bolt. Integral to Gillespie is enlarging the cable end and affixing an outer sleeve thereto; thus, the outer sleeve and the enlarged cable end rotate as a single unit.
After a cable is secured within a borehole, rotation of the cable in either direction releases necessary, or stores undesirable, potential energy; thus, an advantage of the present invention removes this storage or release of potential energy by allowing the independent rotation of each of the tension cylinder and the cable, thereby allowing of the full strength of the cable to support the mine roof.